New experimental finding of dangerous autonomic ganglia changes in cardiac injury following subarachnoid hemorrhage; a reciprocal culprit-victim relationship between the brain and heart

OBJECTIVE

The vagal, stellate, and cardiac ganglia cells changes following subarachnoid hemorrhage (SAH) may occur. This study aimed to investigate if there is any relation between vagal network/stellate ganglion and intrinsic cardiac ganglia insult following SAH.

MATERIALS AND METHODS

Twenty-six rabbits were used in this study. Animals were randomly divided as control (GI, n = 5); SHAM 0.75 cc of saline-injected (n = 5) and study with autologous 1.5 cc blood injection into their cisterna magna(GIII, n = 15). All animals were followed for three weeks and then decapitated. Their motor vagal nucleus, nodose, stellate, and intracardiac ganglion cells were estimated by stereological methods and compared statistically.

RESULTS

Numerical documents of heart-respiratory rates, vagal nerve- ICG, and stellate neuron densities as follows: 276 ± 32/min-22 ± 3/min-10.643 ± 1.129/mm3-4 ± 1/mm3-12 ± 3/mm3 and 2 ± 1/cm3 in the control group; 221 ± 22/min-16 ± 4/min-8.699 ± 976/mm3-24 ± 9/mm3-103 ± 32/mm3 and 11 ± 3/cm3 in the SHAM group; and 191 ± 23/min-17 ± 4/min-9.719 ± 932/mm3-124 ± 31/mm3-1.542 ± 162/mm3 and 32 ± 9/cm3 in the SAH (study) group. The animals with burned neuro-cardiac web had more neurons of stellate ganglia and a less normal neuron density of nodose ganglia (p < 0.005).

CONCLUSION

Sypathico-parasympathetic imbalance induced vagal nerve-ICG disruption following SAH could be named as Burned Neurocardiac Web syndrome in contrast to broken heart because ICG/parasympathetic network degeneration could not be detected in classic broken heart syndrome. It was noted that cardiac ganglion degeneration is more prominent in animals' severe degenerated neuron density of nodose ganglia. We concluded that the cardiac ganglia network knitted with vagal-sympathetic-somatosensitive fibers has an important in heart function following SAH. The neurodegeneration of the cardiac may occur in SAH, and cause sudden death.Graphical abstract[Formula: see text].

TRPV1 enhances cholecystokinin signaling in primary vagal afferent neurons and mediates the central effects on spontaneous glutamate release in the NTS

The gut peptide cholecystokinin (CCK) is released during feeding and promotes satiation by increasing excitation of vagal afferent neurons that innervate the upper gastrointestinal tract. Vagal afferent neurons express CCK1 receptors (CCK1Rs) in the periphery and at central terminals in the nucleus of the solitary tract (NTS). While the effects of CCK have been studied for decades, CCK receptor signaling and coupling to membrane ion channels are not entirely understood. Previous findings have implicated L-type voltage-gated calcium channels as well as transient receptor potential (TRP) channels in mediating the effects of CCK, but the lack of selective pharmacology has made determining the contributions of these putative mediators difficult. The nonselective ion channel transient receptor potential vanilloid subtype 1 (TRPV1) is expressed throughout vagal afferent neurons and controls many forms of signaling, including spontaneous glutamate release onto NTS neurons. Here we tested the hypothesis that CCK1Rs couple directly to TRPV1 to mediate vagal signaling using fluorescent calcium imaging and brainstem electrophysiology. We found that CCK signaling at high concentrations (low-affinity binding) was potentiated in TRPV1-containing afferents and that TRPV1 itself mediated the enhanced CCK1R signaling. While competitive antagonism of TRPV1 failed to alter CCK1R signaling, TRPV1 pore blockade or genetic deletion (TRPV1 KO) significantly reduced the CCK response in cultured vagal afferents and eliminated its ability to increase spontaneous glutamate release in the NTS. Together, these results establish that TRPV1 mediates the low-affinity effects of CCK on vagal afferent activation and control of synaptic transmission in the brainstem.NEW & NOTEWORTHY Cholecystokinin (CCK) signaling via the vagus nerve reduces food intake and produces satiation, yet the signaling cascades mediating these effects remain unknown. Here we report that the capsaicin receptor transient receptor potential vanilloid subtype 1 (TRPV1) potentiates CCK signaling in the vagus and mediates the ability of CCK to control excitatory synaptic transmission in the nucleus of the solitary tract. These results may prove useful in the future development of CCK/TRPV1-based therapeutic interventions.

Ontogeny and Trophic Factor Sensitivity of Gastrointestinal Projecting Vagal Sensory Cell Types

Vagal sensory neurons (VSNs) located in the nodose ganglion provide information, such as stomach stretch or the presence of ingested nutrients, to the caudal medulla via specialized cell types expressing unique marker genes. Here, we leverage VSN marker genes identified in adult mice to determine when specialized vagal subtypes arise developmentally and the trophic factors that shape their growth. Experiments to screen for trophic factor sensitivity revealed that brain-derived neurotrophic factor (BDNF) and glial cell-derived neurotrophic factor (GDNF) robustly stimulate neurite outgrowth from VSNs in vitro Perinatally, BDNF was expressed by neurons of the nodose ganglion itself, while GDNF was expressed by intestinal smooth muscle cells. Thus, BDNF may support VSNs locally, whereas GDNF may act as a target-derived trophic factor supporting the growth of processes at distal innervation sites in the gut. Consistent with this, expression of the GDNF receptor was enriched in VSN cell types that project to the gastrointestinal tract. Last, the mapping of genetic markers in the nodose ganglion demonstrates that defined vagal cell types begin to emerge as early as embryonic day 13, even as VSNs continue to grow to reach gastrointestinal targets. Despite the early onset of expression for some marker genes, the expression patterns of many cell type markers appear immature in prenatal life and mature considerably by the end of the first postnatal week. Together, the data support location-specific roles for BDNF and GDNF in stimulating VSN growth, and a prolonged perinatal timeline for VSN maturation in male and female mice.

Diabetes mellitus differently affects electrical membrane properties of vagal afferent neurons of rats

To study whether diabetes mellitus (DM) would cause electrophysiological alterations in nodose ganglion (NG) neurons, we used patch clamp and intracellular recording for voltage and current clamp configuration, respectively, on cell bodies of NG from rats with DM. Intracellular microelectrodes recording, according to the waveform of the first derivative of the action potential, revealed three neuronal groups (A₀ , A_inf , and C_inf ), which were differently affected. Diabetes only depolarized the resting potential of A₀ (from -55 to -44 mV) and C_inf (from -49 to -45 mV) somas. In A_inf neurons, diabetes increased action potential and the after-hyperpolarization durations (from 1.9 and 18 to 2.3 and 32 ms, respectively) and reduced dV/dt_desc (from -63 to -52 V s^-1 ). Diabetes reduced the action potential amplitude while increasing the after-hyperpolarization amplitude of C_inf neurons (from 83 and -14 mV to 75 and -16 mV, respectively). Using whole cell patch clamp recording, we observed that diabetes produced an increase in peak amplitude of sodium current density (from -68 to -176 pA pF^-1 ) and displacement of steady-state inactivation to more negative values of transmembrane potential only in a group of neurons from diabetic animals (DB2). In the other group (DB1), diabetes did not change this parameter (-58 pA pF^-1 ). This change in sodium current did not cause an increase in membrane excitability, probably explainable by the alterations in sodium current kinetics, which are also induced by diabetes. Our data demonstrate that diabetes differently affects membrane properties of different nodose neuron subpopulations, which likely have pathophysiological implications for diabetes mellitus.

Topographical organization and morphology of substance P (SP)-immunoreactive axons in the whole stomach of mice

Nociceptive afferents innervate the stomach and send signals centrally to the brain and locally to stomach tissues. Nociceptive afferents can be detected with a variety of different markers. In particular, substance P (SP) is a neuropeptide and is one of the most commonly used markers for nociceptive nerves in the somatic and visceral organs. However, the topographical distribution and morphological structure of SP-immunoreactive (SP-IR) axons and terminals in the whole stomach have not yet been fully determined. In this study, we labeled SP-IR axons and terminals in flat mounts of the ventral and dorsal halves of the stomach of mice. Flat-mount stomachs, including the longitudinal and circular muscular layers and the myenteric ganglionic plexus, were processed with SP primary antibody followed by fluorescent secondary antibody and then scanned using confocal microscopy. We found that (1) SP-IR axons and terminals formed an extensive network of fibers in the muscular layers and within the ganglia of the myenteric plexus of the whole stomach. (2) Many axons that ran in parallel with the long axes of the longitudinal and circular muscles were also immunoreactive for the vesicular acetylcholine transporter (VAChT). (3) SP-IR axons formed very dense terminal varicosities encircling individual neurons in the myenteric plexus; many of these were VAChT immunoreactive. (4) The regional density of SP-IR axons and terminals in the muscle and myenteric plexus varied in the following order from high to low: antrum-pylorus, corpus, fundus, and cardia. (5) In only the longitudinal and circular muscles, the regional density of SP-IR axon innervation from high to low were: antrum-pylorus, corpus, cardia, and fundus. (6) The innervation patterns of SP-IR axons and terminals in the ventral and dorsal stomach were comparable. Collectively, our data provide for the first time a map of the distribution and morphology of SP-IR axons and terminals in the whole stomach with single-cell/axon/synapse resolution. This work will establish an anatomical foundation for functional mapping of the SP-IR axon innervation of the stomach and its pathological remodeling in gastrointestinal diseases.

Estrogen-dependent KCa1.1 modulation is essential for retaining neuroexcitation of female-specific subpopulation of myelinated Ah-type baroreceptor neurons in rats

Female-specific subpopulation of myelinated Ah-type baroreceptor neurons (BRNs) in nodose ganglia is the neuroanatomical base of sexual-dimorphic autonomic control of blood pressure regulation, and KCa1.1 is a key player in modulating the neuroexcitation in nodose ganglia. In this study we investigated the exact mechanisms underlying KCa1.1-mediated neuroexcitation of myelinated Ah-type BRNs in the presence or absence of estrogen. BRNs were isolated from adult ovary intact (OVI) or ovariectomized (OVX) female rats, and identified electrophysiologically and fluorescently. Action potential (AP) and potassium currents were recorded using whole-cell recording. Consistently, myelinated Ah-type BRNs displayed a characteristic discharge pattern and significantly reduced excitability after OVX with narrowed AP duration and faster repolarization largely due to an upregulated iberiotoxin (IbTX)-sensitive component; the changes in AP waveform and repetitive discharge of Ah-types from OVX female rats were reversed by G1 (a selective agonist for estrogen membrane receptor GPR30, 100 nM) and/or IbTX (100 nM). In addition, the effect of G1 on repetitive discharge could be completely blocked by G15 (a selective antagonist for estrogen membrane receptor GPR30, 3 μM). These data suggest that estrogen deficiency by removing ovaries upregulates KCa1.1 channel protein in Ah-type BRNs, and subsequently increases AP repolarization and blunts neuroexcitation through estrogen membrane receptor signaling. Intriguingly, this upregulated KCa1.1 predicted electrophysiologically was confirmed by increased mean fluorescent intensity that was abolished by estrogen treatment. These electrophysiological findings combined with immunostaining and pharmacological manipulations reveal the crucial role of KCa1.1 in modulation of neuroexcitation especially in female-specific subpopulation of myelinated Ah-type BRNs and extend our current understanding of sexual dimorphism of neurocontrol of BP regulation.

Brain-gut communication: vagovagal reflexes interconnect the two "brains"

The gastrointestinal tract has its own "brain," the enteric nervous system or ENS, that executes routine housekeeping functions of digestion. The dorsal vagal complex in the central nervous system (CNS) brainstem, however, organizes vagovagal reflexes and establishes interconnections between the entire neuroaxis of the CNS and the gut. Thus, the dorsal vagal complex links the "CNS brain" to the "ENS brain." This brain-gut connectome provides reflex adjustments that optimize digestion and assimilation of nutrients and fluid. Vagovagal circuitry also generates the plasticity and adaptability needed to maintain homeostasis to coordinate among organs and to react to environmental situations. Arguably, this dynamic flexibility provided by the vagal circuitry may, in some circumstances, lead to or complicate maladaptive disorders.

Comparative Analysis of Dorsal Root, Nodose and Sympathetic Ganglia for the Development of New Analgesics

Interoceptive and exteroceptive signals, and the corresponding coordinated control of internal organs and sensory functions, including pain, are received and orchestrated by multiple neurons within the peripheral, central and autonomic nervous systems. A central aim of the present report is to obtain a molecularly informed basis for analgesic drug development aimed at peripheral rather than central targets. We compare three key peripheral ganglia: nodose, sympathetic (superior cervical), and dorsal root ganglia in the rat, and focus on their molecular composition using next-gen RNA-Seq, as well as their neuroanatomy using immunocytochemistry and in situ hybridization. We obtained quantitative and anatomical assessments of transmitters, receptors, enzymes and signaling pathways mediating ganglion-specific functions. Distinct ganglionic patterns of expression were observed spanning ion channels, neurotransmitters, neuropeptides, G-protein coupled receptors (GPCRs), transporters, and biosynthetic enzymes. The relationship between ganglionic transcript levels and the corresponding protein was examined using immunohistochemistry for select, highly expressed, ganglion-specific genes. Transcriptomic analyses of spinal dorsal horn and intermediolateral cell column (IML), which form the termination of primary afferent neurons and the origin of preganglionic innervation to the SCG, respectively, disclosed pre- and post-ganglionic molecular-level circuits. These multimodal investigations provide insight into autonomic regulation, nodose transcripts related to pain and satiety, and DRG-spinal cord and IML-SCG communication. Multiple neurobiological and pharmacological contexts can be addressed, such as discriminating drug targets and predicting potential side effects, in analgesic drug development efforts directed at the peripheral nervous system.

Altered physiology of gastrointestinal vagal afferents following neurotrauma

The adaptability of the central nervous system has been revealed in several model systems. Of particular interest to central nervous system-injured individuals is the ability for neural components to be modified for regain of function. In both types of neurotrauma, traumatic brain injury and spinal cord injury, the primary parasympathetic control to the gastrointestinal tract, the vagus nerve, remains anatomically intact. However, individuals with traumatic brain injury or spinal cord injury are highly susceptible to gastrointestinal dysfunctions. Such gastrointestinal dysfunctions attribute to higher morbidity and mortality following traumatic brain injury and spinal cord injury. While the vagal efferent output remains capable of eliciting motor responses following injury, evidence suggests impairment of the vagal afferents. Since sensory input drives motor output, this review will discuss the normal and altered anatomy and physiology of the gastrointestinal vagal afferents to better understand the contributions of vagal afferent plasticity following neurotrauma.

Morphological identification of thoracolumbar spinal afferent nerve endings in mouse uterus

Major sensory innervation to the uterus is provided by spinal afferent nerves, whose cell bodies lie predominantly in thoracolumbar dorsal root ganglia (DRG). While the origin of the cell bodies of uterine spinal afferents is clear, the identity of their sensory endings has remained unknown. Hence, our major aim was to identify the location, morphology, and calcitonin gene-related peptide (CGRP)-immunoreactivity of uterine spinal afferent endings supplied by thoracolumbar DRG. We also sought to determine the degree of uterine afferent innervation provided by the vagus nerve. Using an anterograde tracing technique, nulliparous female C57BL/6 mice were injected unilaterally with biotinylated dextran into thoracolumbar DRG (T13-L3). After 7-9 days, uterine horns were stained to visualize traced nerve axons and endings immunoreactive to CGRP. Whole uteri from a separate cohort of animals were injected with retrograde neuronal tracer (DiI) and dye uptake in nodose ganglia was examined. Anterogradely labeled axons innervated each uterine horn, these projected rostrally or caudally from their site of entry, branching to form varicose endings in the myometrium and/or vascular plexus. Most spinal afferent endings were CGRP-immunoreactive and morphologically classified as "simple-type." Rarely, uterine nerve cell bodies were labeled in nodose ganglia. Here, we provide the first detailed description of spinal afferent nerve endings in the uterus of a vertebrate. Distinct morphological types of spinal afferent nerve endings were identified throughout multiple anatomical layers of the uterine wall. Compared to other visceral organs, uterine spinal afferent endings displayed noticeably less morphological diversity. Few neurons in nodose ganglia innervate the uterus.

Cannabidiol activation of vagal afferent neurons requires TRPA1

Vagal afferent neurons abundantly express excitatory transient receptor potential (TRP) channels, which strongly influence afferent signaling. Cannabinoids have been identified as direct agonists of TRP channels, including TRPA1 and TRPV1, suggesting that exogenous cannabinoids may influence vagal signaling via TRP channel activation. The diverse therapeutic effects of electrical vagus nerve stimulation also result from administration of the nonpsychotropic cannabinoid, cannabidiol (CBD); however, the direct effects of CBD on vagal afferent signaling remain unknown. We investigated actions of CBD on vagal afferent neurons, using calcium imaging and electrophysiology. CBD produced strong excitatory effects in neurons expressing TRPA1. CBD responses were prevented by removal of bath calcium, ruthenium red, and the TRPA1 antagonist A967079, but not the TRPV1 antagonist SB366791, suggesting an essential role for TRPA1. These pharmacological experiments were confirmed using genetic knockouts where TRPA1 KO mice lacked CBD responses, whereas TRPV1 knockout (KO) mice exhibited CBD-induced activation. We also characterized CBD-provoked inward currents at resting potentials in vagal afferents expressing TRPA1 that were absent in TRPA1 KO mice, but persisted in TRPV1 KO mice. CBD also inhibited voltage-activated sodium conductances in A-fiber, but not in C-fiber afferents. To simulate adaptation, resulting from chronic cannabis use, we administered cannabis extract vapor daily for 3 wk. Cannabis exposure reduced the magnitude of CBD responses, likely due to a loss of TRPA1 signaling. Together, these findings detail a novel excitatory action of CBD at vagal afferent neurons, which requires TRPA1 and may contribute to the vagal mimetic effects of CBD and adaptation following chronic cannabis use.NEW & NOTEWORTHY CBD usage has increased with its legalization. The clinical efficacy of CBD has been demonstrated for conditions including some forms of epilepsy, depression, and anxiety that are also treatable by vagus nerve stimulation. We found CBD exhibited direct excitatory effects on vagal afferent neurons that required TRPA1, were augmented by TRPV1, and attenuated following chronic cannabis vapor exposure. These effects may contribute to vagal mimetic effects of CBD and adaptation after chronic cannabis use.

Unique Molecular Characteristics of Visceral Afferents Arising from Different Levels of the Neuraxis: Location of Afferent Somata Predicts Function and Stimulus Detection Modalities

Viscera receive innervation from sensory ganglia located adjacent to multiple levels of the brainstem and spinal cord. Here we examined whether molecular profiling could be used to identify functional clusters of colon afferents from thoracolumbar (TL), lumbosacral (LS), and nodose ganglia (NG) in male and female mice. Profiling of TL and LS bladder afferents was also performed. Visceral afferents were back-labeled using retrograde tracers injected into proximal and distal regions of colon or bladder, followed by single-cell qRT-PCR and analysis via an automated hierarchical clustering method. Genes were chosen for assay (32 for bladder; 48 for colon) based on their established role in stimulus detection, regulation of sensitivity/function, or neuroimmune interaction. A total of 132 colon afferents (from NG, TL, and LS ganglia) and 128 bladder afferents (from TL and LS ganglia) were analyzed. Retrograde labeling from the colon showed that NG and TL afferents innervate proximal and distal regions of the colon, whereas 98% of LS afferents only project to distal regions. There were clusters of colon and bladder afferents, defined by mRNA profiling, that localized to either TL or LS ganglia. Mixed TL/LS clustering also was found. In addition, transcriptionally, NG colon afferents were almost completely segregated from colon TL and LS neurons. Furthermore, colon and bladder afferents expressed genes at similar levels, although different gene combinations defined the clusters. These results indicate that genes implicated in both homeostatic regulation and conscious sensations are found at all anatomic levels, suggesting that afferents from different portions of the neuraxis have overlapping functions.SIGNIFICANCE STATEMENT Visceral organs are innervated by sensory neurons whose cell bodies are located in multiple ganglia associated with the brainstem and spinal cord. For the colon, this overlapping innervation is proposed to facilitate visceral sensation and homeostasis, where sensation and pain are mediated by spinal afferents and fear and anxiety (the affective aspects of visceral pain) are the domain of nodose afferents. The transcriptomic analysis performed here reveals that genes implicated in both homeostatic regulation and pain are found in afferents across all ganglia types, suggesting that conscious sensation and homeostatic regulation are the result of convergence, and not segregation, of sensory input.

Blunted Vagal Cocaine- and Amphetamine-Regulated Transcript Promotes Hyperphagia and Weight Gain

The vagus nerve conveys gastrointestinal cues to the brain to control eating behavior. In obesity, vagally mediated gut-brain signaling is disrupted. Here, we show that the cocaine- and amphetamine-regulated transcript (CART) is a neuropeptide synthesized proportional to the food consumed in vagal afferent neurons (VANs) of chow-fed rats. CART injection into the nucleus tractus solitarii (NTS), the site of vagal afferent central termination, reduces food intake. Conversely, blocking endogenous CART action in the NTS increases food intake in chow-fed rats, and this requires intact VANs. Viral-mediated Cartpt knockdown in VANs increases weight gain and daily food intake via larger meals and faster ingestion rate. In obese rats fed a high-fat, high-sugar diet, meal-induced CART synthesis in VANs is blunted and CART antibody fails to increase food intake. However, CART injection into the NTS retains its anorexigenic effect in obese rats. Restoring disrupted VAN CART signaling in obesity could be a promising therapeutic approach.

Premature ventricular contractions activate vagal afferents and alter autonomic tone: implications for premature ventricular contraction-induced cardiomyopathy

Mechanisms behind development of premature ventricular contraction (PVC)-induced cardiomyopathy remain unclear. PVCs may adversely modulate the autonomic nervous system to promote development of heart failure. Afferent neurons in the inferior vagal (nodose) ganglia transduce cardiac activity and modulate parasympathetic output. Effects of PVCs on cardiac parasympathetic efferent and vagal afferent neurotransmission are unknown. The purpose of this study was to evaluate effects of PVCs on vagal afferent neurotransmission and compare these effects with a known powerful autonomic modulator, myocardial ischemia. In 16 pigs, effects of variably coupled PVCs on heart rate variability (HRV) and vagal afferent neurotransmission were evaluated. Direct nodose neuronal recordings were obtained in vivo, and cardiac-related afferent neurons were identified based on their response to cardiovascular interventions, including ventricular chemical and mechanical stimuli, left anterior descending (LAD) coronary artery occlusion, and variably coupled PVCs. On HRV analysis before versus after PVCs, parasympathetic tone decreased (normalized high frequency: 83.6 ± 2.8 to 72.5 ± 5.3; P < 0.05). PVCs had a powerful impact on activity of cardiac-related afferent neurons, altering activity of 51% of neurons versus 31% for LAD occlusion (P < 0.05 vs. LAD occlusion and all other cardiac interventions). Both chemosensitive and mechanosensitive neurons were activated by PVCs, and their activity remained elevated even after cessation of PVCs. Cardiac afferent neural responses to PVCs were greater than any other intervention, including ischemia of similar duration. These data suggest that even brief periods of PVCs powerfully modulate vagal afferent neurotransmission, reflexly decreasing parasympathetic efferent tone.NEW & NOTEWORTHY Premature ventricular contractions (PVCs) are common in many patients and, at an increased burden, are known to cause heart failure. This study determined that PVCs powerfully modulate cardiac vagal afferent neurotransmission (exerting even greater effects than ventricular ischemia) and reduce parasympathetic efferent outflow to the heart. PVCs activated both mechano- and chemosensory neurons in the nodose ganglia. These peripheral neurons demonstrated adaptation in response to PVCs. This study provides additional data on the potential role of the autonomic nervous system in PVC-induced cardiomyopathy.

Loss of Vagal Sensitivity to Cholecystokinin in Rats Born with Intrauterine Growth Retardation and Consequence on Food Intake

Perinatal malnutrition is associated with low birth weight and an increased risk of developing metabolic syndrome in adulthood. Modification of food intake (FI) regulation was observed in adult rats born with intrauterine growth retardation induced by maternal dietary protein restriction during gestation and maintained restricted until weaning. Gastrointestinal peptides and particularly cholecystokinin (CCK) play a major role in short-term regulation of FI by relaying digestive signals to the hindbrain via the vagal afferent nerve (VAN). We hypothesized that vagal sensitivity to CCK could be affected in rats suffering from undernutrition [low protein (LP)] during fetal and postnatal life, leading to an altered gut-brain communication and impacting satiation. Our aim was to study short-term FI along with signals of appetite and satiation in adult LP rats compared to control rats. The dose-response to CCK injection was investigated on FI as well as the associated signaling pathways activated in nodose ganglia. We showed that LP rats have a reduced first-meal satiety ratio after a fasting period associated to a higher postprandial plasmatic CCK release, a reduced sensitivity to CCK when injected at low concentration and a reduced presence of CCK-1 receptor in nodose ganglia. Accordingly, the lower basal and CCK-induced phosphorylation of calcium/calmodulin-dependent protein kinase in nodose ganglia of LP rats could reflect an under-expressed vanilloid family of transient receptor potential cation channels on VAN. Altogether, the present data demonstrated a reduced vagal sensitivity to CCK in LP rats at adulthood, which could contribute to deregulation of FI reported in this model.

Role of satellite glial cells in gastrointestinal pain

Gastrointestinal (GI) pain is a common clinical problem, for which effective therapy is quite limited. Sensations from the GI tract, including pain, are mediated largely by neurons in the dorsal root ganglia (DRG), and to a smaller extent by vagal afferents emerging from neurons in the nodose/jugular ganglia. Neurons in rodent DRG become hyperexcitable in models of GI pain (e.g., gastric or colonic inflammation), and can serve as a source for chronic pain. Glial cells are another element in the pain signaling pathways, and there is evidence that spinal glial cells (microglia and astrocytes) undergo activation (gliosis) in various pain models and contribute to pain. Recently it was found that satellite glial cells (SGCs), the main type of glial cells in sensory ganglia, might also contribute to chronic pain in rodent models. Most of that work focused on somatic pain, but in several studies GI pain was also investigated, and these are discussed in the present review. We have shown that colonic inflammation induced by dinitrobenzene sulfonic acid (DNBS) in mice leads to the activation of SGCs in DRG and increases gap junction-mediated coupling among these cells. This coupling appears to contribute to the hyperexcitability of DRG neurons that innervate the colon. Blocking gap junctions (GJ) in vitro reduced neuronal hyperexcitability induced by inflammation, suggesting that glial GJ participate in SGC-neuron interactions. Moreover, blocking GJ by carbenoxolone and other agents reduces pain behavior. Similar changes in SGCs were also found in the mouse nodose ganglia (NG), which provide sensory innervation to most of the GI tract. Following systemic inflammation, SGCs in these ganglia were activated, and displayed augmented coupling and greater sensitivity to the pain mediator ATP. The contribution of these changes to visceral pain remains to be determined. These results indicate that although visceral pain is unique, it shares basic mechanisms with somatic pain, suggesting that therapeutic approaches to both pain types may be similar. Future research in this field should include additional types of GI injury and also other types of visceral pain.

Molecular and cellular mechanisms that initiate pain and itch

Somatosensory neurons mediate our sense of touch. They are critically involved in transducing pain and itch sensations under physiological and pathological conditions, along with other skin-resident cells. Tissue damage and inflammation can produce a localized or systemic sensitization of our senses of pain and itch, which can facilitate our detection of threats in the environment. Although acute pain and itch protect us from further damage, persistent pain and itch are debilitating. Recent exciting discoveries have significantly advanced our knowledge of the roles of membrane-bound G protein-coupled receptors and ion channels in the encoding of information leading to pain and itch sensations. This review focuses on molecular and cellular events that are important in early stages of the biological processing that culminates in our senses of pain and itch.

Opening of pannexin- and connexin-based channels increases the excitability of nodose ganglion sensory neurons

Satellite glial cells (SGCs) are the main glia in sensory ganglia. They surround neuronal bodies and form a cap that prevents the formation of chemical or electrical synapses between neighboring neurons. SGCs have been suggested to establish bidirectional paracrine communication with sensory neurons. However, the molecular mechanism involved in this cellular communication is unknown. In the central nervous system (CNS), astrocytes present connexin43 (Cx43) hemichannels and pannexin1 (Panx1) channels, and the opening of these channels allows the release of signal molecules, such as ATP and glutamate. We propose that these channels could play a role in glia-neuron communication in sensory ganglia. Therefore, we studied the expression and function of Cx43 and Panx1 in rat and mouse nodose-petrosal-jugular complexes (NPJcs) using confocal immunofluorescence, molecular and electrophysiological techniques. Cx43 and Panx1 were detected in SGCs and in sensory neurons, respectively. In the rat and mouse, the electrical activity of vagal nerve increased significantly after nodose neurons were exposed to a Ca²⁺/Mg²⁺-free solution, a condition that increases the open probability of Cx hemichannels. This response was partially mimicked by a cell-permeable peptide corresponding to the last 10 amino acids of Cx43 (TAT-Cx43CT). Enhanced neuronal activity was reduced by Cx hemichannel, Panx1 channel and P2X₇ receptor blockers. Moreover, the role of Panx1 was confirmed in NPJc, because in those from Panx1 knockout mice showed a reduced increase of neuronal activity induced by Ca²⁺/Mg²⁺-free extracellular conditions. The data suggest that Cx hemichannels and Panx channels serve as paracrine communication pathways between SGCs and neurons by modulating the excitability of sensory neurons.

Development of the vagal innervation of the gut: steering the wandering nerve

BACKGROUND

The vagus nerve is the major neural connection between the gastrointestinal tract and the central nervous system. During fetal development, axons from the cell bodies of the nodose ganglia and the dorsal motor nucleus grow into the gut to find their enteric targets, providing the vagal sensory and motor innervations respectively. Vagal sensory and motor axons innervate selective targets, suggesting a role for guidance cues in the establishment of the normal pattern of enteric vagal innervation.

PURPOSE

This review explores known molecular mechanisms that guide vagal innervation in the gastrointestinal tract. Guidance and growth factors, such as netrin-1 and its receptor, deleted in colorectal cancer, extracellular matrix molecules, such as laminin-111, and members of the neurotrophin family of molecules, such as brain-derived neurotrophic factor have been identified as mediating the guidance of vagal axons to the fetal mouse gut. In addition to increasing our understanding of the development of enteric innervation, studies of vagal development may also reveal clinically relevant insights into the underlying mechanisms of vago-vagal communication with the gastrointestinal tract.

Alterations in N-methyl-D-aspartate receptor subunits in primary sensory neurons following acid-induced esophagitis in cats

The excitatory amino acid glutamate plays an important role in the development of neuronal sensitization and the ionotropic N-methyl-d-aspartate receptor (NMDAR) is one of the major receptors involved. The objective of this study was to use a cat model of gastroesophageal reflux disease (GERD) to investigate the expression of the NR1 and NR2A subunits of NMDAR in the vagal and spinal afferent fibers innervating the esophagus. Two groups of cats (Acid-7D and PBS-7D) received 0.1 N HCl (pH 1.2) or 0.1 M PBS (pH 7.4) infusion in the esophagus (1 ml/min for 30 min/day for 7 days), respectively. NR1 splice variants (both NH(2) and COOH terminals) and NR2A in the thoracic dorsal root ganglia (DRGs), nodose ganglia (NGs), and esophagus were evaluated by RT-PCR, Western blot, and immunohistochemistry. Acid produced marked inflammation and a significant increase in eosinophil peroxidase and myeloperoxidase contents compared with PBS-infused esophagus. The NR1-4 splice variant gene exhibited a significant upregulation in DRGs and esophagus after acid infusion. In DRGs, NGs, and esophagus, acid infusion resulted in significant upregulation of NR1 and downregulation of NR2A subunit gene expression. A significant increase in NR1 polypeptide expression was observed in DRGs and NGs from Acid-7D compared with control. In conclusion, long-term acid infusion in the cat esophagus resulted in ulcerative esophagitis and differential expressions of NR1 and NR2A subunits. It is possible that these changes may in part contribute to esophageal hypersensitivity observed in reflux esophagitis.

Anandamide induces cough in conscious guinea-pigs through VR1 receptors

1. Endogenous neuronal lipid mediator anandamide, which can be synthesized in the lung, is a ligand of both cannabinoid (CB) and vanilloid receptors (VR). The tussigenic effect of anandamide has not been studied. The current study was designed to test the direct tussigenic effect of anandamide in conscious guinea-pigs, and its effect on VR1 receptor function in isolated primary guinea-pig nodose ganglia neurons. 2. Anandamide (0.3-3 mg.ml(-1)), when given by aerosol, induced cough in conscious guinea-pigs in a concentration dependent manner. When guinea-pigs were pretreated with capsazepine, a VR1 antagonist, the anandamide-induced cough was significantly inhibited. Pretreatment with CB1 (SR 141716A) and CB2 (SR 144528) antagonists had no effect on anandamide-induced cough. These results indicate that anandamide-induced cough is mediated through the activation of VR1 receptors. 3. Anandamide (10-100 micro M) increased intracellular Ca(2+) concentration estimated by Fluo-4 fluorescence change in isolated guinea-pig nodose ganglia cells. The anandamide-induced Ca(2+) response was inhibited by two different VR1 antagonists: capsazepine (1 micro M) and iodo-resiniferatoxin (I-RTX, 0.1 micro M), indicating that anandamide-induced Ca(2+) response was through VR1 channel activation. In contrast, the CB1 (SR 141716A, 1 micro M) and CB2 (SR 144528, 0.1 micro M) receptor antagonists had no effect on Ca(2+) response to anandamide. 4. In conclusion, these results provide evidence that anandamide activates native vanilloid receptors in isolated guinea-pig nodose ganglia cells and induces cough through activation of VR1 receptors.